442 lines
12 KiB
Go
442 lines
12 KiB
Go
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package ssh
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import (
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"bytes"
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"errors"
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"fmt"
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"io"
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)
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// clientAuthenticate authenticates with the remote server. See RFC 4252.
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func (c *connection) clientAuthenticate(config *ClientConfig) error {
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// initiate user auth session
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if err := c.transport.writePacket(Marshal(&serviceRequestMsg{serviceUserAuth})); err != nil {
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return err
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}
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packet, err := c.transport.readPacket()
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if err != nil {
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return err
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}
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var serviceAccept serviceAcceptMsg
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if err := Unmarshal(packet, &serviceAccept); err != nil {
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return err
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}
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// during the authentication phase the client first attempts the "none" method
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// then any untried methods suggested by the server.
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tried := make(map[string]bool)
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var lastMethods []string
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for auth := AuthMethod(new(noneAuth)); auth != nil; {
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ok, methods, err := auth.auth(c.transport.getSessionID(), config.User, c.transport, config.Rand)
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if err != nil {
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return err
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}
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if ok {
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// success
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return nil
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}
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tried[auth.method()] = true
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if methods == nil {
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methods = lastMethods
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}
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lastMethods = methods
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auth = nil
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findNext:
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for _, a := range config.Auth {
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candidateMethod := a.method()
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if tried[candidateMethod] {
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continue
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}
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for _, meth := range methods {
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if meth == candidateMethod {
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auth = a
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break findNext
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}
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}
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}
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}
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return fmt.Errorf("ssh: unable to authenticate, attempted methods %v, no supported methods remain", keys(tried))
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}
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func keys(m map[string]bool) []string {
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s := make([]string, 0, len(m))
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for key := range m {
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s = append(s, key)
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}
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return s
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}
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// An AuthMethod represents an instance of an RFC 4252 authentication method.
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type AuthMethod interface {
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// auth authenticates user over transport t.
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// Returns true if authentication is successful.
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// If authentication is not successful, a []string of alternative
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// method names is returned. If the slice is nil, it will be ignored
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// and the previous set of possible methods will be reused.
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auth(session []byte, user string, p packetConn, rand io.Reader) (bool, []string, error)
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// method returns the RFC 4252 method name.
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method() string
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}
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// "none" authentication, RFC 4252 section 5.2.
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type noneAuth int
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func (n *noneAuth) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
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if err := c.writePacket(Marshal(&userAuthRequestMsg{
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User: user,
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Service: serviceSSH,
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Method: "none",
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})); err != nil {
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return false, nil, err
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}
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return handleAuthResponse(c)
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}
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func (n *noneAuth) method() string {
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return "none"
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}
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// passwordCallback is an AuthMethod that fetches the password through
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// a function call, e.g. by prompting the user.
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type passwordCallback func() (password string, err error)
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func (cb passwordCallback) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
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type passwordAuthMsg struct {
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User string `sshtype:"50"`
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Service string
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Method string
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Reply bool
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Password string
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}
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pw, err := cb()
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// REVIEW NOTE: is there a need to support skipping a password attempt?
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// The program may only find out that the user doesn't have a password
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// when prompting.
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if err != nil {
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return false, nil, err
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}
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if err := c.writePacket(Marshal(&passwordAuthMsg{
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User: user,
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Service: serviceSSH,
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Method: cb.method(),
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Reply: false,
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Password: pw,
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})); err != nil {
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return false, nil, err
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}
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return handleAuthResponse(c)
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}
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func (cb passwordCallback) method() string {
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return "password"
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}
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// Password returns an AuthMethod using the given password.
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func Password(secret string) AuthMethod {
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return passwordCallback(func() (string, error) { return secret, nil })
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}
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// PasswordCallback returns an AuthMethod that uses a callback for
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// fetching a password.
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func PasswordCallback(prompt func() (secret string, err error)) AuthMethod {
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return passwordCallback(prompt)
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}
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type publickeyAuthMsg struct {
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User string `sshtype:"50"`
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Service string
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Method string
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// HasSig indicates to the receiver packet that the auth request is signed and
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// should be used for authentication of the request.
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HasSig bool
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Algoname string
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PubKey []byte
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// Sig is tagged with "rest" so Marshal will exclude it during
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// validateKey
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Sig []byte `ssh:"rest"`
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}
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// publicKeyCallback is an AuthMethod that uses a set of key
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// pairs for authentication.
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type publicKeyCallback func() ([]Signer, error)
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func (cb publicKeyCallback) method() string {
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return "publickey"
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}
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func (cb publicKeyCallback) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
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// Authentication is performed in two stages. The first stage sends an
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// enquiry to test if each key is acceptable to the remote. The second
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// stage attempts to authenticate with the valid keys obtained in the
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// first stage.
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signers, err := cb()
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if err != nil {
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return false, nil, err
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}
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var validKeys []Signer
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for _, signer := range signers {
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if ok, err := validateKey(signer.PublicKey(), user, c); ok {
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validKeys = append(validKeys, signer)
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} else {
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if err != nil {
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return false, nil, err
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}
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}
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}
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// methods that may continue if this auth is not successful.
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var methods []string
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for _, signer := range validKeys {
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pub := signer.PublicKey()
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pubKey := pub.Marshal()
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sign, err := signer.Sign(rand, buildDataSignedForAuth(session, userAuthRequestMsg{
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User: user,
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Service: serviceSSH,
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Method: cb.method(),
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}, []byte(pub.Type()), pubKey))
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if err != nil {
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return false, nil, err
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}
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// manually wrap the serialized signature in a string
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s := Marshal(sign)
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sig := make([]byte, stringLength(len(s)))
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marshalString(sig, s)
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msg := publickeyAuthMsg{
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User: user,
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Service: serviceSSH,
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Method: cb.method(),
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HasSig: true,
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Algoname: pub.Type(),
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PubKey: pubKey,
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Sig: sig,
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}
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p := Marshal(&msg)
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if err := c.writePacket(p); err != nil {
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return false, nil, err
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}
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var success bool
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success, methods, err = handleAuthResponse(c)
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if err != nil {
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return false, nil, err
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}
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if success {
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return success, methods, err
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}
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}
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return false, methods, nil
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}
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// validateKey validates the key provided is acceptable to the server.
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func validateKey(key PublicKey, user string, c packetConn) (bool, error) {
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pubKey := key.Marshal()
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msg := publickeyAuthMsg{
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User: user,
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Service: serviceSSH,
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Method: "publickey",
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HasSig: false,
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Algoname: key.Type(),
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PubKey: pubKey,
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}
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if err := c.writePacket(Marshal(&msg)); err != nil {
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return false, err
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}
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return confirmKeyAck(key, c)
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}
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func confirmKeyAck(key PublicKey, c packetConn) (bool, error) {
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pubKey := key.Marshal()
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algoname := key.Type()
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for {
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packet, err := c.readPacket()
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if err != nil {
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return false, err
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}
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switch packet[0] {
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case msgUserAuthBanner:
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// TODO(gpaul): add callback to present the banner to the user
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case msgUserAuthPubKeyOk:
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var msg userAuthPubKeyOkMsg
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if err := Unmarshal(packet, &msg); err != nil {
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return false, err
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}
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if msg.Algo != algoname || !bytes.Equal(msg.PubKey, pubKey) {
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return false, nil
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}
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return true, nil
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case msgUserAuthFailure:
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return false, nil
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default:
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return false, unexpectedMessageError(msgUserAuthSuccess, packet[0])
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}
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}
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}
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// PublicKeys returns an AuthMethod that uses the given key
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// pairs.
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func PublicKeys(signers ...Signer) AuthMethod {
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return publicKeyCallback(func() ([]Signer, error) { return signers, nil })
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}
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// PublicKeysCallback returns an AuthMethod that runs the given
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// function to obtain a list of key pairs.
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func PublicKeysCallback(getSigners func() (signers []Signer, err error)) AuthMethod {
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return publicKeyCallback(getSigners)
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}
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// handleAuthResponse returns whether the preceding authentication request succeeded
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// along with a list of remaining authentication methods to try next and
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// an error if an unexpected response was received.
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func handleAuthResponse(c packetConn) (bool, []string, error) {
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for {
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packet, err := c.readPacket()
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if err != nil {
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return false, nil, err
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}
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switch packet[0] {
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case msgUserAuthBanner:
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// TODO: add callback to present the banner to the user
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case msgUserAuthFailure:
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var msg userAuthFailureMsg
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if err := Unmarshal(packet, &msg); err != nil {
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return false, nil, err
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}
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return false, msg.Methods, nil
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case msgUserAuthSuccess:
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return true, nil, nil
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case msgDisconnect:
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return false, nil, io.EOF
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default:
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return false, nil, unexpectedMessageError(msgUserAuthSuccess, packet[0])
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}
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}
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}
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// KeyboardInteractiveChallenge should print questions, optionally
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// disabling echoing (e.g. for passwords), and return all the answers.
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// Challenge may be called multiple times in a single session. After
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// successful authentication, the server may send a challenge with no
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// questions, for which the user and instruction messages should be
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// printed. RFC 4256 section 3.3 details how the UI should behave for
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// both CLI and GUI environments.
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type KeyboardInteractiveChallenge func(user, instruction string, questions []string, echos []bool) (answers []string, err error)
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// KeyboardInteractive returns a AuthMethod using a prompt/response
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// sequence controlled by the server.
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func KeyboardInteractive(challenge KeyboardInteractiveChallenge) AuthMethod {
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return challenge
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}
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func (cb KeyboardInteractiveChallenge) method() string {
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return "keyboard-interactive"
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}
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func (cb KeyboardInteractiveChallenge) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
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type initiateMsg struct {
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User string `sshtype:"50"`
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Service string
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Method string
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Language string
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Submethods string
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}
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if err := c.writePacket(Marshal(&initiateMsg{
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User: user,
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Service: serviceSSH,
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Method: "keyboard-interactive",
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})); err != nil {
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return false, nil, err
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}
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for {
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packet, err := c.readPacket()
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if err != nil {
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return false, nil, err
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}
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// like handleAuthResponse, but with less options.
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switch packet[0] {
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case msgUserAuthBanner:
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// TODO: Print banners during userauth.
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continue
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case msgUserAuthInfoRequest:
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// OK
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case msgUserAuthFailure:
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var msg userAuthFailureMsg
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if err := Unmarshal(packet, &msg); err != nil {
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return false, nil, err
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}
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return false, msg.Methods, nil
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case msgUserAuthSuccess:
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return true, nil, nil
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default:
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return false, nil, unexpectedMessageError(msgUserAuthInfoRequest, packet[0])
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}
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var msg userAuthInfoRequestMsg
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if err := Unmarshal(packet, &msg); err != nil {
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return false, nil, err
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}
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// Manually unpack the prompt/echo pairs.
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rest := msg.Prompts
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var prompts []string
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var echos []bool
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for i := 0; i < int(msg.NumPrompts); i++ {
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|
|
prompt, r, ok := parseString(rest)
|
||
|
|
if !ok || len(r) == 0 {
|
||
|
|
return false, nil, errors.New("ssh: prompt format error")
|
||
|
|
}
|
||
|
|
prompts = append(prompts, string(prompt))
|
||
|
|
echos = append(echos, r[0] != 0)
|
||
|
|
rest = r[1:]
|
||
|
|
}
|
||
|
|
|
||
|
|
if len(rest) != 0 {
|
||
|
|
return false, nil, errors.New("ssh: extra data following keyboard-interactive pairs")
|
||
|
|
}
|
||
|
|
|
||
|
|
answers, err := cb(msg.User, msg.Instruction, prompts, echos)
|
||
|
|
if err != nil {
|
||
|
|
return false, nil, err
|
||
|
|
}
|
||
|
|
|
||
|
|
if len(answers) != len(prompts) {
|
||
|
|
return false, nil, errors.New("ssh: not enough answers from keyboard-interactive callback")
|
||
|
|
}
|
||
|
|
responseLength := 1 + 4
|
||
|
|
for _, a := range answers {
|
||
|
|
responseLength += stringLength(len(a))
|
||
|
|
}
|
||
|
|
serialized := make([]byte, responseLength)
|
||
|
|
p := serialized
|
||
|
|
p[0] = msgUserAuthInfoResponse
|
||
|
|
p = p[1:]
|
||
|
|
p = marshalUint32(p, uint32(len(answers)))
|
||
|
|
for _, a := range answers {
|
||
|
|
p = marshalString(p, []byte(a))
|
||
|
|
}
|
||
|
|
|
||
|
|
if err := c.writePacket(serialized); err != nil {
|
||
|
|
return false, nil, err
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|